This from the "Off" manufacturer's product FAQ:
Q. Can I spray Off! Skintastic Family Care personal insect repellents on clothing?
A. Off! insect repellents will not damage cotton, wool or nylon fabrics. You should avoid spraying Off! Skintastic Family Care insect repellents on acetate, rayon, spandex or other synthetic fabrics.
So still use with caution if you are thinking about applying it to your gear.
I read a while ago about stress tests done on various fabrics that DEET had been applied to. It was a US climbing organisation I think. If I recall correctly, pure DEET itself was did not cause issues with the fabrics tested but in solutions at lower concentrations (the kind of stuff typical off the shelf) did, and it was thought that it was other oil based solvents present in the solution that were weakening the fabrics. Had a quick search and can't find a link but I'm sure you'd be able to dig it up.
I've had success with the insect repellent clothing (several pairs of covertable pants) I've used which has had permeation applied in manufacturing. It doesn't seem to be effective for the length of use claimed - a few washes and the effect is gone. This kinds of garments are probably the go if heading into extremely buggy conditions. Don't know if this can be applied aftermarket and if so if it is as effective.
Hopefully the new repellents that have been in the news lately are safe to use on gear and hit the market in the not too distant future.